Yawn

A yawn is a physiologic reflex that involves a large, long taking in of air, the stretching of eardrums as the jaw opens wide, and last a (sometimes loud) breathing out. Pandiculation is the act of yawning and stretching simultaneously. Most of us yawn and stretch (pandiculation) when we wake up or go to bed, yawn when we are bored or when we need to “pop” our ears after traveling in high altitudes, and even yawn just because we saw someone else yawn.

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Yawning Infant

Yawning in other animals

• The act of yawning (oscitation) occurs in almost all vertebrates- even birds and fish exhibit a form of mouth gaping similar to yawning.
• In humans, yawning can start as early as 20 weeks after conception.

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Panthera leo yawn

What is a yawn?

A yawn is a coordinated movement of the thoracic muscles in the chest, diaphragm, larynx in the throat, and palate in the mouth. By yawning, we help distribute surfactant (wetting agent) to coat the alveoli (tiny air sacs) in the lungs.

Yawning on command

• Generally speaking, we cannot yawn on command.
• It is theorized that yawning is a semi-voluntary action and partly a reflex controlled by neurotransmitters in the hypothalamus of the brain.
• It is also associated with increased levels of neurotransmitters, neuropeptide proteins and certain hormones.

Positive feedback

• Yawning is commonly associated with tiredness, stress, overwork, lack of stimulation and boredom.
• In humans, yawning is often triggered by others yawning (e.g. seeing a person yawning, talking to someone on the phone who is yawning) and is a typical example of positive feedback.

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Stewart-yawn

Contagiousness

The yawn reflex has long been observed to be contagious. In 1508, Erasmus wrote, "One man's yawning makes another yawn. Contagious yawning comes from witnessing someone or thinking about another person yawning.

• According to studies (Platek, et al), 42-55% of human adults will yawn during, or after, watching a video tape of another person repeatedly yawning.
• It typically happens in older normal well-adjusted human beings.
• Traditionally, it is not seen in humans under five or people with autism.

The immediate cause for contagious yawning may be the mirror neurons in the frontal cortex of certain vertebrates, which, upon being exposed to a stimulus, activates the same regions in the brain.

• Mirror neurons have been proposed as a driving force for imitation which lies at the root of much human learning such as language acquisition.
• Yawning may be an offshoot of the same imitative impulse.

Joseph Ducreux (French) - Self-Portrait, Yawning

Outside temperature

• Dr. Andrew Gallup and Omar Tonsi Eldakar (2011) discovered that outside temperature might also affect the amount of yawning as well. 
• If the outside temperature is warmer than normal, then the organism yawns less frequently. 
• A possible explanation of this is that because the air outside is useless to the organism it does not need to suck in more oxygen through yawning. 
• However, other tests showed that the amount of yawning increased when both outside temperature and the temperature of the brain increased.

There are also sociological and evolutionary biological based explanations.

Yawning Image

Link to circadian rhythm

• Yawning might be linked to our circadian rhythms (biological activity related to a 24 hour cycle) as a signal to go to bed or as a waking ritual.
• It might be as a way to transmit boredom or feelings of stress to the social group.

Reasons, functions

Charles Darwin argued, in The Expression of the Emotions in Man and Animals, that if a behaviour was present in many cultures, then it must be inherited (wholly or partly). All traits which appear in a wide range of animals must have some function which is supported (or was supported) by natural selection.

History and theories of yawning

• There are numerous theories on why we yawn and scientists have yet to come to any consensus. One of the first theories for yawning can be traced back to Hippocrates, the father of medicine, who hypothesized that yawning precedes a fever and is a way to remove bad air from the lungs.
• Based on modern evidence, however, it seems unlikely that yawning serves as a function of the respiratory system.
• By the 17th and 18th centuries scientists were challenging the Hippocratic theories of yawning.
• These new theories focused on the circulatory system, suggesting that yawning causes an increase in blood pressure, heart rate and oxygen in the blood, which in turn improves motor function and alertness.
• This might explain why many athletes yawn before playing their respective sports.
• Yet, current tests have shown that the heart rate, sweating or brain’s electrical activity do not increase after yawning.
• Today, scientists continue to research the function(s) of yawning.
• Pioneer researcher on contagious behavior Dr. Robert Provine suggests that yawning is “associated with the change of a behavioral state- wakefulness to sleep, sleep to wakefulness, boredom to alertness(Provine, 2005).”
• And more recent studies have suggested that yawning might be connected to brain temperature (Gallup and Gallup, 2008).
• When the brain becomes warmer than the homeostatic (stable) temperature, we might yawn to cool the brain.
• It is theorized that cooler blood from the body floods into the brain and the warm blood circulates out through the jugular vein.

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